Much progress has been made in the study of single molecule electrical transport (1, 2). Reports, particularly of two-terminal structures, are increasingly robust and reproducible (3, 4, 5, 6). Molecular properties are highly dependent on details of structure and composition. Recent theoretical and experimental work has shown that transport properties too can change enormously as a result of atom-level structural variations (7, 8, 9, 10, 11, 12). It is clear that the full potential of molecular devices will be unveiled only when meticulous structural knowledge and control is in hand.
It is equally vital that strategies for gating (electrostatic control of current through a device) be improved. Gated devices—such as vacuum tube “valves” and transistors—are desirable because they allow dynamic reconfiguration of current flow in circuits. One problem inherent to studying gated molecular conduction is that there simply is insufficient space to have three electrodes converge on a volume the size of, for example, a benzene molecule (13). A compromise can be made—connect two closely spaced electrodes to the molecule while a third necessarily more distant electrode serves as a gate—but poor gate efficiency results (10, 14). A radically different approach appears to be required.
Current three-terminal single molecule device schemes have focused on phenomena such as Kondo resonance or single electron (Coulomb blockade) physics that require cryogenic conditions to operate (15, 16). An alternate scheme, capable of room temperature switching behavior, is a prerequisite (but not sufficient) quality for molecular electronics to advance.
While active molecular technologies face many additional challenges, the need for detailed structural control, for strategies to achieve gated molecular conduction, and for room temperature operation are the most substantial obstacles to be overcome.
One way to satisfy these requirements is to study molecules bound to order surfaces, such as silicon, with using scanning tunneling with quantum mechanical (17) and classical electrostatic simulations and analysis. In this way, atomic structure and electrostatic potential variations that affect the properties of an individual molecule are understood. In spite of efforts to understand and ultimately control electroconductivity on an atomic scale, systematic and controlled building of devices on this scale has proven difficult.
Thus, there exists a need for an electrostatically regulated atomic scale electroconductivity device, such as a molecular transistor. Additionally, there exists a need for a process to build such a device that is amenable to manufacturing and a variety of operating environments.